From a LM/MM point of view, the CN consists of two domains, a CS domain and a PS domain or one of these domains. Each domain has its own service state machine. An UE, that is supporting both CS services and PS services, has a CS service state machine and a PS service state machine. The two peers of the service state machine are working independently to each other, although associated to the same UE. The UE-CN signalling aims to keep the peer entities synchronised. As an introduction, Figure 6.1 gives an overview of the UE registration and connection principles for the CN consisting of two separate PS and CS service nodes.

The CN consists of both a CS domain with MSC/VLR, 3G_MSC/VLR, as the main serving node and an PS domain with SGSN/GGSN, 3G_SGSN, 3G GGSN, MME, S-GW and P-GW as the main serving nodes. The main PS service states are PS-DETACHED, PS-IDLE and PS-CONNECTED. The main CS service states are CS DETACHED, CS-IDLE and CS-CONNECTED. For the respective domain there are specific related MM system information controlling the MM functionality of the UE. When the UE is attached to PS it may be registered with SGSN and MME in parallel. The aim of the RAN is to offer one unified set of radio bearers which can be used for bursty packet traffic and for traditional telephony traffic. Therefore, only one logical control channel structure is used for all kind of traffic. The radio resource handling is RAN internal functionality and the CN does not define the type of radio resource allocated. The UTRAN and the E-UTRAN Radio Resource Control (RRC) has two modes, RRC Connected mode and RRC Idle mode. The RRC mode describes which identity is used to identify the UE. In RRC Idle mode the UE is identified by a CN associated identity. In RRC Connected mode the UE is assigned a Radio Network Temporary Identity to be used as UE identity on common transport channels. When the UE is allocated dedicated UTRAN transport channels, it uses the inherent addressing provided by these transport channels. In PS-CONNECTED state the UE is in RRC Connected mode. In CS-CONNECTED state the UE is in RRC Connected mode. For the mobility functionality, different area concepts are used. Tracking Areas (TAs), Location Areas (LAs) and Routing Areas (RAs) are used in the CN. UTRAN Registration Areas and Cell Areas are used in the Iu based RAN. LAs are related to CS services. TAs and RAs are related to PS services. When "Intra Domain Connection of RAN Nodes to Multiple CN Nodes" is not used, one LA is handled by one CN node. With "Intra Domain Connection of RAN Nodes to Multiple CN Nodes" one LA may be handled by multiple CN nodes. For an UE that is registered in a LA, this implies that the UE is registered in the specific CN node handling this specific LA. When "Intra Domain Connection of RAN Nodes to Multiple CN Nodes" is not used, one RA is handled by one CN node. With "Intra Domain Connection of RAN Nodes to Multiple CN Nodes" one RA may be handled by multiple CN nodes. One TA may be handled by multiple CN nodes. For an UE that is registered in a TA or RA, this implies that the UE is registered in the specific CN node handling this specific TA or RA. LA is used by the 3G_MSC/VLR for paging the UE. RA is used by the SGSN for paging the UE. TA is used by the MME for paging the UE. UTRAN Registration Areas and Cell Areas are only visible in the UTRAN and used in RRC-Connected mode. The relations between LA, TA and RA are described in clause 4.3.2. In RRC Idle mode it is the broadcast MM system information (e.g. information about the present LA, present TA or present RA) that determines when the UE initiates a location registration procedure towards the CN. An UE crossing an LA border, in state CS-IDLE and RRC Idle mode, shall initiate LA update towards the MSC. An UE crossing an RA border, in state PS-IDLE and RRC Idle mode, shall initiate RA update towards the SGSN. An UE crossing a TA border to a TA that is not registered with the MME, in state ECM Idle or ECM Connected, shall initiate TA update towards the MME. In UTRAN RRC Connected mode, the UE receives the MM system information on the established RRC connection. (i.e. the broadcast MM system information is not used by the UE in the UTRAN RRC connected mode). In E-UTRAN RRC Connected mode, the UE receives the broadcast MM system information and uses it. An UE receiving information indicating a new LA, in state CS-IDLE and RRC Connected mode, shall initiate LA update towards the MSC. An UE receiving information indicating a new RA, in state PS-IDLE and RRC Connected mode, shall initiate RA update towards the SGSN. An UE receiving information indicating a new TA that is not registered with the MME shall initiate TA update towards the MME. An UE in state CS-CONNECTED and RRC Connected mode, shall not initiate LA update towards the CN. In CS-DETACHED mode the UE shall not initiate any LA update and this independent of the RRC mode. In PS-DETACHED mode the UE shall not initiate any TA or RA updates and this independent of the RRC mode. In addition to normal location registration when changing registration area, the UE may (network options) perform CS periodic registration when in CS-IDLE state and PS periodic registration when in PS-IDLE state. The respective periodic registration may be on/off on LA respective TA or RA level. On the MM level, IMSI and CS related TMSI are used as UE identities in the CS domain, and IMSI and PS related TMSI are used as UE identities in the PS domain. The IMSI is the common UE identity for the two CN domains (CS and PS). A signalling connection between the UE and the CN refers to a logical connection consisting of an RRC connection between UE and RAN and an Iu or S1 signalling connection between the RAN and the CN node. The CS domain related signalling between RAN and CN applies to UTRAN only. The CS domain related signalling and PS domain related signalling uses one common RRC connection and two Iu signalling connections ("two RANAP instances"), i.e. one Iu signalling connection for the CS domain and one Iu signalling connection for the PS domain.

The use of separated PS and CS mobility mechanisms within the UE and within the CN can lead to non-optimal usage of the radio resource (for example a UE in PS idle and CS idle state would perform both LA updates (for the CS mechanism) and TA or RA updates (for PS mechanisms)). To offer flexibility in the provision of MM , combined mechanisms can be used for LM purposes as well as for attach/detach status purposes. A UE can perform combined update mechanisms. A CN should allow combined update operations (operator option). UEs should support the use of both combined and separate mechanisms. The RAN does not co-ordinate MM procedures that are logically between the CN and the MS. This includes: LM, authentication, temporary identity management and equipment identity check.